`bevy_platform::prelude` items are not available in other modules

I noticed that in the `prelude` module of `bevy_platform`, there are items exclusively there. That is uncommon as using `prelude` is generally optional to get a quick import done.

https://dev-docs.bevy.org/bevy_platform/prelude/index.html

The docs of `prelude` here seem to try to fulfill another purpose, migrating from `std` to `no_std`, I guess? We might then maybe want to rename the module to something else.